The story sounds a bit bull because of the compute power and the ways you'd have to screw with data lines at memory speeds and not introduce noise and not make the system massively unstable to make it a thing - it'd be easier just to screw with firmware like the NSA did with Cisco gear. If this is real then China is way way ahead of the west in both subversive technologies and technology in general and I have a hard time believing it. It's not that it's not a thing so much as how large the chip would have to be to do what's claimed, look at something like a PHY for display port and consider the chip would have to be more complex than that. Exactly. People would notice.
That said it's not really the company so much as the Chinese government infiltrating the company that is the risk. No reason SMC would ever have to know any more that Gemalto or Cisco or anybody else would. That being said you'd also have to mess with various design and QA processes - basically SMC would have to never inspect any boards going out the factory and coming back under RMA etc or do any continuous improvement to not be complicit if it's actually a thing..
It all sounds a bit miniformationy to me and I'm definitely *not* a tinfoil hatter.